Yes, I know many people has uploaded this game's video on YouTube however last times some people can't believe the game works on regular ZX Spectrum 128K.

So it works. Therefore this video is different than others: on the beginning I loaded Computer Tester to display what machine is that (ZX Spectrum 128+). Then I reset it and loaded DOOM game via diskdrive.

Yes, it slows down when a hero opens the door (it's because Russian Spectrum - Pentagon - has a bit more tacts on its 3,5Mhz CPU) but still works fine on normal ZX Spectrum 128 and its 3,5Mhz CPU.